The invention relates to a method of producing molten metal, in particular pig iron or steel pre-products, from at least partially fine-particulate metal carriers, in particular partially reduced or reduced sponge iron, in a melter gasifier. Carbon-containing material and oxygen or an oxygen-containing gas are supplied to the melter gasifier with simultaneous formation of a reducing gas in a bed formed of solid carbon carriers. The metal carriers are melted, optionally upon previous complete reduction. The present invention also relates to a melter gasifier for carrying out the method.
From EP-B-0 010 627 it is known to feed particulate iron-containing material, such as pre-reduced sponge iron, through a centrally arranged charging opening in the hood of a melter gasifier. The particles drop into the melter gasifier by the effect of gravity and slow their descent in the fluidized bed existing within the melter gasifier. Coal in lumpy form is charged through a charging opening arranged laterally in the hood of the melter gasifier or in a dome covering the melter gasifier towards a top, also under the influence of gravity. The reducing gas formed in the melter gasifier is withdrawn through the centrally arranged charging opening for the iron-containing material.
A process of this kind is not suitable for processing fine-particle metal carriers, in particular fine-particle sponge iron. The pronounced gas flow of the reducing gas formed in the gasification zone and withdrawn through the central charging opening arranged in the hood or in the dome of the melter gasifier carries the fine-particle metal carriers out of the melter gasifier. The temperature in the upper region of the melter gasifier, i.e. in the region above the gasification zone, is too low to ensure a melt-down, thereby contributing to an unwanted discharge of the fine-particle metal carriers. A higher temperature would provide agglomeration of the fine particles at the charging site to form bigger particles which in spite of the ascending gas stream could sink down into the gasification zone.
From EP-A -0 217 331 it is known to introduce pre-reduced fine ore into a melter gasifier and to completely reduce and melt it by means of a plasma burner while supplying a carbon-containing reducing agent. The pre-reduced fine ore or the song-iron powder respectively is fed to a plasma burner provided in the lower section of the melter gasifier. A disadvantage of this method is that by supplying the pre-reduced fine ore directly in the lower meltdown region, i.e. in the region where the melt collects, complete reduction can no longer be ensured and the chemical composition necessary for further processing the pig iron cannot be achieved. Moreover, the charging of major amounts of pre-reduced fine or is not feasible due to a fluidized or fixed bed formed from coal in the lower region of the melter gasifier. The fluidized or fixed bed prevents removal of a sufficient quantity of the melting products from the high-temperature zone of the plasma burner. The charging of major amounts of pre-reduced fine ore would lead to instant thermal and mechanical failure of the plasma burner.
From EP-B-0 111 176 it is known to feed a fine grain fraction of sponge iron particles into the melter gasifier through a downpipe projecting from the head of the melter gasifier into the proximity of the coal fluidized bed. At the end of the downpipe a baffle plate is provided for minimizing the velocity of the fine grain fraction, resulting in a very low exit velocity of the fine grain fraction from the downpipe. At the charging site, the temperature in the melter gasifier is very low, whereby immediate melting of the supplied fine grain fraction is prevented. This and the low exit velocity from the downpipe cause a substantial portion of the supplied fine grain fraction to be carried out of the melter gasifier again together with the reducing gas generated in the same. The charging of a major amount of sponge iron particles containing a fine portion or of only a fine grain fraction is not feasible in accordance with this method.
From EP-A-0 594 557 it is known to charge a fine grain fraction of sponge iron by means of a conveying gas directly into the fluidized bed formed by the gasification zone in the melter gasifier. However, this procedure is disadvantageous, since the gas circulation of the fluidized bed may be disturbed to form obstructions of the fluidized bed. The fluidized bed acts like a filter and the obstructions can ensue as a consequence of the fine grain fraction that is blown directly into the fluidized bed. As a result, eruptive outbreaks of gas may occur which will break up the clogged fluidized bed. Hereby, the gasification process for the carbon carriers and also the melt-down process for the reduced iron ore are markedly disturbed.
From EP-A-0 576 414 it is known to feed fine-particle metal carriers into the gasification zone via dust burners. This method exhibits a poor melt-in performance, which is due to a short dwelling time of the particles in the hot flame.
The invention aims to avoid these disadvantages and difficulties and has as its object to provide a method of the kind initially described as well as a melter gasifier for carrying out the method. According to the present invention the processing of fine-particulate metal carriers can be conducted without the need for briquetting. The present invention reliably avoids discharging supplied fine-particulate metal carriers, optionally in pre-reduced or in completely reduced condition, by the reducing gas produced in the melter gasifier. The present invention also ensures complete reduction, which may optionally be required, of the fine particles. It is a particular object of the invention to provide a method enabling the processing of a majority of a charge, preferably 100%, of which is/are made up of fine-particulate iron-containing material provided to pig iron and/or steel prematerial utilizing a melter gasifier.
With a method of the initially described kind, the above objects are achieved in that the fine-particulate metal carriers are charged to a high-temperature combustion zone maintained by a combustion process. The carriers, optionally upon complete reduction, are melted in the high-temperature combustion zone which is spatially isolated from the freeboard of the melter gasifier that is located above the bed and extends into the bed. The offgases formed in the high-temperature combustion zone exit by passing through at least a portion of the bed. The offgases are also cooled in the bed and are withdrawn from the melter gasifier along with the reducing gas formed within the bed.
A melter gasifier for carrying out the method according to the present invention has feed ducts for oxygen-containing gases, carbon carriers and metal carriers. The melter gasifier has at least one gas discharge duct for discharging a reducing gas produced in a bed of the melter gasifier. The reducing gas produced from the bed is formed of solid carbon carriers departing from the bed. The melter gasifier includes a tap for the metal melt and a tap for slag with at least one feed duct for feeding fine-particulate metal carriers. The feed duct opens into at least one high-temperature combustion chamber that is spatially isolated form the interior of the melter gasifier. The feed duct has a mouth that projects into the bed formed of solid carbon carriers and is provided with a burner.
To assure easy access to the high-temperature combustion chamber as well as a long service life of the same, the high-temperature combustion chamber is advantageously constructed as a wall that departs from the dome of the melter gasifier, is open at the bottom, cylindrical in shape and provided with a refractory material.
A simple construction for the chamber includes a single high-temperature combustion chamber, which is arranged centrally and with its longitudinal axis lying in the vertical longitudinal axis of the melter gasifier.
Advantageously, the high-temperature combustion chamber projects outward at its upper end through the dome of the melter gasifier. The feed duct for fine-particulate metal carriers runs into the high-temperature combustion chamber at this exterior end. The burner is arranged centrally at an outer end of the feed duct, whereby repair work to be done on the burner or exchange of the same is feasible in an easy manner.
An ideal structure of the bed is attainable if according to a preferred embodiment feed ducts for carbon carriers project through the dome of the melter gasifier at a radial distance from the high-temperature combustion chamber.
The service life can be further increased if the wall of the high-temperature combustion chamber is provided with an internal wall cooling. The wall of the high-temperature combustion chamber is accordingly equipped with finned tubes through which a cooling medium flows and the tubes are provided with a refractory lining on both sides. At the upper end and at the lower end of the high-temperature combustion chamber there are suitably provided ring-shaped headers for a cooling medium, preferably cooling water, each being integrated into the wall of the high-temperature combustion chamber.
At its end projecting outward through the dome of the melter gasifier, the high-temperature combustion chamber suitably is provided with a removable cover and the burner and the feed duct are arranged in the cover.
It is beneficial to the melt process if the burner is formed by a fine-coal/oxygen burner.